(a) Field of the Invention
The present invention relates to a digital cable television broadcasting system. More specifically, the present invention relates to a restricted reception device for chargeable broadcasting services, and a reception system and method for a digital broadcasting system using the restricted reception device.
(b) Description of the Related Art
Conventionally, cable television (TV) broadcasting has provided fundamental audio and video services in the traditional analog system, but with the digitalization of broadcasting systems, the cable broadcasting system now also provides bi-directional audiovisual TV services as well as multimedia services. In particular, a digital cable broadcasting system in Korea that satisfies the requirements of the international standard, the OpenCable standard, is scheduled to provide services in the near future.
In Korea, chargeable TV services are largely classified into a cable broadcasting service and a satellite broadcasting service. The digital cable broadcasting system, which basically provides bi-directional services using a cable network, is much more advantageous in providing various services than the satellite broadcasting system that provides bi-directional services using a PSTN (Public Switched Telephone Network) or a PSDN (Public Switched Data Network).
FIG. 1 is a block diagram of a digital cable broadcasting system that is a general bi-directional broadcasting transceiver system.
The digital cable broadcasting system of the OpenCable standard has, as shown in FIG. 1, channels that are largely divided into a broadcasting channel (called “in-band channel” herein) for transmission of broadcasting data, and a bi-directional channel (called “out-of-band channel” herein) for transmission/reception of auxiliary data for broadcasting, or bi-directional communication data.
This broadcasting system comprises a broadcasting service provider 101 for providing audio/video data; a bi-directional service provider 102 for providing bi-directional contents; a broadcasting network adaptor 103 for constituting a broadcasting signal and sending it to the cable network; a bi-directional network adaptor 104 for performing bi-directional communication with cable subscribers, transmission of auxiliary data, and management of subscriber receivers; a broadcasting transmission medium 105 composed of an optical cable and a coaxial cable; a bi-directional network 106 for establishing a communication network such as ATM (Asynchronous Transfer Mode) or IP (Internet Protocol) through the cable network; and a subscriber receiver 107 for receiving broadcasting and bi-directional services.
The subscriber receiver 107 comprises a network interface unit 108 including a broadcasting network interface module 110 for receiving a broadcasting signal from the cable network, and a bi-directional network interface module 111 for sending and receiving bi-directional data; and a broadcasting reception unit 109 including a restricted reception module 112 for converting the broadcasting signal to audible/visible audio/video or data, and restricting the reception of the audiovisual data for chargeable broadcasting services.
In the above-constructed digital cable system, broadcasting programs are transferred on the in-band channels, and channel/program guide information and data related to restricted reception are transferred on the out-of-band channels. In regard to the restricted reception, in satellite broadcasting, ECM (Entitlement Control Message) and EMM (Entitlement Management Message) are transferred with the broadcasting data on the in-band channels. But, in cable broadcasting of the OpenCable standard, the ECM is transferred on the in-band channels for broadcasting data, and the EMM is transferred on the out-of-band channels for auxiliary data or bi-directional communication data. Specifically, the restricted reception system of cable broadcasting sends the EMM to the individual corresponding subscribers, which enables more efficient subscriber control.
The restricted reception system of the MPEG-2 (Moving Picture Experts Group-2) standard is used for satellite broadcasting. But the MPEG-2 restricted reception system is inapplicable to cable broadcasting, because ECM and EMM are independently transferred on a different channel as stated above.
The MPEG-2 restricted reception system encodes a control word (CW) for scrambling broadcasting data in the ECM and transfers the encoded CW with a CW-encoding key included in the EMM. Here, the ECM and the EMM are transferred in the form of MPEG-2 TS (Transport Stream) packets having a different packet identifier (PID) value. The PID value is equal to the value specified in the CA_PID field of the CA descriptor in the PMT (Program Map Table) and the CAT (Conditional Access Table) among the PSI (Program Specific Information) tables specified in the MPEG-2 standard.
To make a specific scrambled broadcasting program in the audiovisual form, the receiver detects a TS packet including the PAT table from the broadcasting data stream to parse the PAT table, determines the PID value of the PMT table of the corresponding program, and detects the TS packet having the PID value to parse the PMT table. Then the receiver acquires the PID value of the ECM-including TS packet by analyzing the PMT table, and detects the ECM-including TS packet to acquire the ECM.
On the other hand, decoding of the ECM is necessary in order to acquire the CW from the ECM. The receiver receives the TS packet including the CAT table to parse the CAT table, acquires the PID value of the EMM-including TS packet, and detects the EMM-including TS packet to acquire the EMM.
The receiver extracts an ECM decoding key from the EMM and decodes the ECM using the key to acquire the final CW. The CW thus obtained is transferred to the descrambler of the receiver, where it is used for converting the scrambled broadcasting program in an audiovisual form.
But the above-stated restricted reception method of the MPEG-2 system is impossible to apply to the digital cable broadcasting system of the OpenCable standard. The reason is because the three data transmission systems related to broadcasting on out-of-band channels in the OpenCable standard are different from the data transmission system of the MPEG-2 standard.
The three data transmission systems related to broadcasting through out-of-band channels are DVS-167, DVS-178, and DOCSIS (Data-Over-Cable Service Interface Specifications) systems. Among these methods, the DVS-178 system transmits data in the MPEG-2 TS form in a similar way to the traditional MPEG-2 system, and extracts the ECM and the EMM in the same manner as the MPEG-2 system.
However, the DVS-167 and DOCSIS systems transmit data in the form of ATM cell and IP packet, respectively, rather than MPEG-2 TS, so they cannot acquire the EMM-including PID value by analyzing the CAT table as with the traditional MPEG-2 system.
Moreover, in the OpenCable standard, the EMM is not transmitted for each chargeable service channel by channel, but rather for all the chargeable channels using out-of-band channels. Namely, there is a demand for redefining an EMM data constitution method and an EMM extracting and processing method at the receiver for the sake of restricted reception when using DVS-167 or DOCSIS to transmit data through an out-of-band channel.